I would advise against STR. The added dmg is negligible and so is the aggro you'll get. If you stay with VIT, you give your healer breathing room. They can stay in DPS mode much longer and actually do more DPS than a STR tank. A DPS-mode healer blows away the STR tank dmg.

I have never, ever run into aggro problems on a VIT tank, unless the DPS blows everything at the start of the fight before I get mobs gathered and placed, but even STR won't help there.